1. Field of the Invention
The present invention relates to a capacitive sensor for dynamical quantity for detecting a dynamical physical quantity such as acceleration and angular velocity as a capacitance change and more particularly to a capacitive dynamical quantity sensor which is manufactured through a semiconductor manufacturing process.
2. Description of the Related Art
Heretofore, there has been known an electrostatic capacitive dynamical quantity sensor which has a weight that shifts according to the magnitude of externally applied acceleration or angular velocity, and a beam for supporting the weight formed within a semiconductor substrate, and which serves to detect a change in electrostatic capacitance generated between a movable electrode including the weight and a fixed electrode formed at a minute distance from the movable electrode (refer to JP 8-94666 A, for example). FIG. 9 is a schematic cross-sectional view of the conventional electrostatic capacitive dynamical quantity sensor. In this sensor, weights 91 and beams 92 are formed within a semiconductor substrate 93 through a fine patterning process, and are sealed from both sides by joining an upper substrate 94 and a lower substrate 95. In such an electrostatic capacitive dynamical quantity sensor, in order to have the weight to work as a movable electrode, a part of fixed electrodes 98 has a contact to the semiconductor substrate 93 to control the electrical potential of the weight 91. FIG. 10 is a schematic cross-sectional view of a substrate contact portion. A part of the fixed electrode 98 laminated on a glass substrate 95 is formed so as to extend to a joint area between the glass substrate 95 and the semiconductor substrate 93, and is brought into contact with the semiconductor substrate 93 through the joining. The provision of a contact portion 99 makes it possible to control the electrical potential of the weight 91 formed within the semiconductor substrate 93 (refer to JP 8-94666 A, for example).
The conventional electrostatic capacitive dynamical quantity sensor, however, involves the following problems.
As shown in FIG. 10, an area 100 in which the glass substrate 95 does not contact with the semiconductor substrate 93 is generated in the periphery of the contact portion 99 due to a thickness of the fixed electrode 98 to cause the serious joint failure. This joint failure causes air leakage and the like to degrade the reliability of the device. In addition, it is possible to prevent the reliability degradation by designing a larger joint area in advance to avoid joint failure in the periphery of the contact portion, yet the chip size becomes larger to lead to a higher cost.